Piston



Patented Dec. 13, 1927.

FE HQE.

CLINTON L. WALKER, 0F PIEDMONT, CALIFORNIA.

' PISTON.

Application filed June 21, 1926, Serial No. 117,414. Renewed October 24, 1927.

This invention relates to pistons and particularly that type employed in internal combustion engines.

In the operation of internal combustion engines of the high speed type, it is desirable tomake pistons particularly of the trunk type as light as possible. The use of aluminum or alloys thereof in piston construction has been extensively attempted and solves the problem of weight reduction. Aluminum, however, has a greater coetlicient of expansion than cast iron and as a result considerable clearance must be allowed between the piston and the cylinder wall to allow for the greater expansion of the piston. This leads to poor compression when the engine is cold, leakage of oil and gases, piston slap, etc. Furthermore, aluminum wears exceedingly when highly heated and the clearance or loose fit provided soon becomes too great.

The object of the present invention is to provide a composite piston; that is, apiston consisting of amain body of an aluminum alloy and an exterior shell constructed of cast iron or steel; to provide a piston which will expand or contract in diameter in harmony with the expansion or contraction of the bore of the cylinder; and further. to produce a piston which will have a longer life and ofier better friction conditions.

One form which my invention may assume is exemplified in the following description and illustrated in the accompanying drawings, in which Fig. 1 is a side elevation of the piston showing the application of the cast iron shell.

Fig. 2 is a central vertical section of the piston.

Fig. 3 is Figure 1.

Referring to the drawings in detail and particularly to Figures 1 and 2. A indicates the! head of the piston, B the ring portion, and C the skirt. The ring portion is provided with the usual grooves 2 for the reception of. the piston rings, and the interior of the piston is provided with the usual bosses 3 for the reception of the wrist pin. The skirt portion is in this instance reduced in diameter substantially from end to end for the purpose of receiving a cast iron shell generally indicated at E, and large grooves 7 and 8 are formed at the upper and lower a cross section on line IIIIII,

ends of the reduced portion these grooves being provided with inclined seats as inclicated at 9 and 10. The shell proper may be constructed of cast iron or steel and it is made in two separate halves as indicated at E and F, the line of division between the two halves being shown at 4:. The upper and lower ends of the shell sections E and F are provided with inwardly turned annularly disposed flanges 11 and 11 which engage the seat members 9 and 10 and the exterior surface of the shell sections are grooved as indicated at'12 to receive'babbitt rings as the babbitt is poured into the grooves and is afterward machined and finished to the proper diameter. The co-efiicient of expansion of expansion of aluminum compared with cast iron is 1.9 to 1; that is, aluminum expands nearly twice as much as iron or steel. Hence, if the piston is heated, the gap indicated at L opens upmore than the length of the cast iron shell and it is therefore necessary to compensate for this unequality in expansion between the piston skirt and the shell. This is accomplished by providing the inclined annular seats 8 and 9 and the inturned angularly disposed flanges 11 and 11; that is, the diameter of the skirt portion always increases when the piston is heated and this increase in diameter compensates for the increase in the length of the gap indicated at L. This compensation permits the shell or shoe section s E and F to maintain a constantcontact with the inner walls of the cylinder providing the angle of the seats 9 and 10 is correct. This angle is found from the equation that the tangentof the angle where L is the length of the shoe and E9 and T8 its coefficient of expansion and temperature change, E72 and T3; the eo-etii'cient of expansion and temperature change of the body or trunk portion of the piston and D its diameter, and E0 and T0 the coefficient of expansion and temperature change of the cylinder wall. The temperature changes in the piston shirts, in the shoe and in the cylinder walls would have to be observed under all variations of motor conditions of operation before applying the formulae, the

cold motor. In this case, it will be observed that the trunk portion of the piston will heat up more rapidly than the water jacketed cylinder and the piston shoe which is in contact with it. The change would undoubtedly be nearly the same in the shoes and the cylinder walls as the shoes have contact with the trunk portion of the pistons only at the ends and with the cylinder walls at the rubbing portions of the shoes. When the angle indicated at O is correctly determined the exterior diameter of the shell sections E and F may be turned. to the exact bore of the cylinder with no allowance for expansion as the exterior diameter will remain in constant running contact with the cylinder walls, rcgardless of contraction or ei-ipansion of the aluminum piston skirt. This will produce a quiet running motor. It will reduce piston vibration and weight, the piston will wear longer, and no slap will be encountered when the piston is cold. .The babbitt rings indicated. at 13 are also important as they main tain the cast iron or steel shell out of actual contact with the cylinder wall and as such will offer better friction conditions. and. when wear does occur the babbitt can be renewed without discharging the cast iron shell or the piston proper.

It will be observed that the shell is in con tact with the piston proper only at the bevel end and that the shell remains in constant contact with the cylinder wall. Hence, the shell will assume a temperature about the same as the cylinder wall, thereby pro viding favorable lubricating conditions. A piston of this character can be constructed to be practically as permanent the re maining parts of the engine. For instance, by leaving extra stock between the ring grooves and extra st ck around the wrist pin bosses, wear can be taken up by the use of oversized rings by merely returning the grooves and. by re-rcaming the wrist pin holes and inserting oversizcd wrist pins. The babbittrings in the shell can be renewed from time to time, thus making it unnecessary to discard the pistons with wear.

The babbitt wearing surface oliers better friction conditions and hence it is to be exqected that the cylinder will wear far less than with the conventional type o'tpiston. This longer wearing life oi? the cylinder will also be augmented by reason of: the elimination of piston slap when the pistons are cold.

lVhile certain features of the present in vention are more or less specifically illus trated, I wish it understood that various changes in form and proportion may be resortedto within the scope otthe appended claims. I similarly wish it understood that the materials and finish ol the several parts employed may be such as the experience and judgment of the manufacturer may dictate or various uses may demand.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. A piston comprising a head, a ring and a skirt portion, said skirt portion being reduced in diameter and having oppositely opposed angular seats formed one at the upper and one at the lower end of the skirt, a shell member adapted to bereceived by said reduced portion, and annular inturned flanges on the shell engaging with and supported by the oppoied angular seats, the angle of said seat surfaces to a central transverse plan of the piston being that angle Whose tangent is equal to the longitudinal expansion of the shell member divided by the difference in the diametrical expansionot' the skirt portion of the piston and the bore of the cylinder for any selected period of time involving a ten'iperature change within the cylinder and piston.

2. The combination with a cylinder of a piston, comprising a head, a ring and a shirt portion, said piston being constructed of an aluminum alloy and said skirt portion below the rings having an elongated annular recess formed therein with angular seats at the upper and lower ends of the recess, and a metallic shell adapted to be received in the recess, said shell having angular laces formed at its opposite ends con'lori'ning to the angular seats in the recess, and theanglc employed being that angle whose tangent is equal to the longitudinal expansion of the shell divided by ,the diametrical expansion of the skirt member-minus the diametrical expansion of the cylinder bore for any period of time involving a material temperature change within the cylinder-and piston.

A piston comprising a headand a skirt portion, said skirt portion beingreduccd in diameter and haying oppositely opposed angula r seats formed one at theupper and one at the lower end of the sxirt, a shell member adapted tobe received by said reduccdpon tion, and annular iuturned flanges on the shell engaging with and supported by the opposed angular seats, the angle of said seat surfaces to a central transverse plan of the piston being :that angle whose tangent is equal to the longitudinal expansion oi. the shell member divided by the difference in the diametrical expansion of the skirt portionot' the pistoirand the bore of the cylinder for any selected period of time involving a temperature change within the cylinder and piston.

CLINTON, L. WALKER. 

